It was about a guy whose dad was always away for work so he lived alone with his stepmom, or his mom, and as the laws of hentai dictate they began to have sex after a few chapters the (step)mom started having doubts and told the boy to find a girl his own age, which he did and the (step)mom began to get jealous but the girl ran away because the boy wanted anal and then the boy started having anal sex with his (step)mom at which point the previous girl walked in and said that she would make him normal again.

I either read it on doujin-moe or tadanohito.

Thanks in advance.

This one